Window AC unit will provide the cheapest, easiest no-nonsense raw performance. I ran mine for nearly four days straight and temps didn't budge a degree. Only cons are that I actually found the temps so low that insulation was a pain for a sub-zero newb like myself, and the noise level...rotary compressors are far, far from quiet. Although I really don't like the idea of any sort of water cooler or mini-fridge; they are just too weak. Either a pricey lab chiller, an A/C, or completely built from scratch are the ways to go. Just be forewarned that no type of chiller is exactly a walk in the park...fully insulating took me several days at the least, planning and trial and error.